In recent years the need to remove sulfur oxides from flue gases generated by the combustion of coal has become more apparent. A number of factors have contributed to this need, including the increasingly strong connection between emission of sulfur oxides from coal-fired power plants and the phenomenon of acid rain, which acidifies lakes and is harmful to fish and plant life; the economic need to use coal for generating electricity due to the reduced reliability of low-sulfur oil imports, etc. However, the construction of properly functional liquid scrubbing systems has developed a new set of problems and many millions of dollars have already been expended in attempting to deal with them.
Almost of necessity, scrubbing systems need to be fabricated of metal. It has been found that attempts to construct such systems of ordinary constructional steels or even of common grades of stainless steels have resulted in failure. Thus, coals used for power generation contain varying levels of sulfur, chlorides, fluorides and other impurities which are absorbed within the liquid scrubbing media used to contact the resulting flue gases. Water and chemicals used in the scrubbing process also contribute to the buildup of chlorides within the scrubber. Chloride buildup to quite astonishing levels occurs in recirculating systems which are resorted to in order to minimize water consumption and pollution problems resulting from release of dilute solutions. Chloride concentrations in closed loop systems as high as 50,000 ppm (5%) have been reported.
Alloys are available which have the combinations of properties, including strength, ductility, impact resistance and corrosion resistance required for scrubber service, but the available alloys are expensive. U.S. Pat. Nos. 2,703,277, 3,160,500 and 3,203,792 may be referred to as disclosing alloys useful in scrubber service.
The present invention is directed to provision of alloys suitable for use in scrubber service at a lower cost than that of available alloys.